Have been an appliance tech for 20 years,
First look for the part on line. Not even worth doing anything if you can't get the part. Check www.searspartsdirect.com If not there try www.Reliableparts.com.
Most microwave turntable motors are accessed through the bottom through the light, or another access panel that is removable, but not all. There are some that are not fun to do. Use your eyes and look for a panel or light cover to remove. BESURE IT IS UNPLUGGED FIRST.
I would not use the micro without it, as the food will burn in very select places without it. Microwaves that don't have a turntable have a wave stirrer inside where you can't see it.